[gn] Fix accidental args override from dafffe2

dafffe2 added `"-specialize-decoders-per-bitwidth",` to args,
but also added a stray `args = []` line after it.

Author: nico

llvm/utils/gn/secondary/llvm/lib/Target/AMDGPU/Disassembler/BUILD.gn

@@ -6,8 +6,6 @@ tablegen("AMDGPUGenDisassemblerTables") {
     "-gen-disassembler",
     "-specialize-decoders-per-bitwidth",
   ]
-
-  args = [   ]
   td_file = "../AMDGPU.td"
 }